EP0576450A1

EP0576450A1 - Methylene cyclobutane derivates

Info

Publication number: EP0576450A1
Application number: EP92905642A
Authority: EP
Inventors: Eike Poetsch; Werner Binder; Thomas Geelhaar
Original assignee: Merck Patent GmbH
Current assignee: Merck Patent GmbH
Priority date: 1991-03-16
Filing date: 1992-03-04
Publication date: 1994-01-05
Also published as: JPH06507603A; DE4206771A1; WO1992016483A1; US5384072A

Abstract

Des dérivés de cyclobutane de méthylène ont la formule (I), dans laquelle R1, A1, A2, Z1, Z2, L1, L2, X, Y et m ont la signification donnée dans la première revendication. L'invention concerne également leur utilisation comme composants de milieux de cristaux liquides pour affichages électro-optiques.Cyclobutane derivatives of methylene have the formula (I), in which R1, A1, A2, Z1, Z2, L1, L2, X, Y and m have the meaning given in the first claim. The invention also relates to their use as components of liquid crystal media for electro-optical displays.

Description

Methylene cyclobutane derivatives

The invention relates to methylene cyclobutane derivatives of formula I

Li L2

in which

R ^{1 is} halogen, CN, CF ₃ , -OCF ₃ , -OCF ₂ H or an unsubstituted or an alkyl or alkenyl or substituted simply by CN, halogen or CF ₃

Perfluoroalkyl radical with up to 15 carbon atoms, one or more CH ₂ groups in these radicals each being independent of one another by -S-, - ^> - _/ - \ ζ ^ ~, -0-, -CO-, -CO -0-, -O-CO- or -0-CO-O- can be replaced so that S and / or 0 atoms are not directly linked,

Ai and A ² each independently (a) trans-1,4-cyclohexylene radical, in which one or more non-adjacent CH ₂ groups can also be replaced by -O- and / or -S-,

(b) 1,4-phenylene radical, in which one or two CH groups can also be replaced by N,

(c) radical from the group 1,3-cyclobutylene, 1,3-bicyclo (l, l, l) pentylene, 1,4-cyclohexenylene, 1,4-bicyclo (2,2,2) octylene , Piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydronapthalene-2,6-diyl and 1,2,3-tetrahydronaphthalene-2,6-diyl,

where the residues (a) and (b) can be substituted one or more times by CN or halogen,

L ¹ and L ² each H, F or Cl,

Z ¹ and Z ² each independently of one another -CH ₂ CH ₂ -, -C≡C-, -CH ₂ 0-, -OCH ₂ -, -CO-O-, -O-CO-, -CH = N-, -N = CH-,

-CH ₂ S-, -SCH ₂ -, a single bond or one

Alkylene group with 3 to 6 carbon atoms, where also a CH ₂ group can be replaced by -0-, -C0-0-, -O-CO-, -CHHalogen- or -CHCN-.

X and Y are each independently of one another F, Cl, Br, CF ₃ , CN, C0 ₂ alkyl or alkyl having 1 to 6 carbon atoms, one of the radicals X and Y also H, and m 0, 1, 2 or 3

mean,

with the proviso that when m = 0, A ² 1,4-phenylene and Z ^{2 are} a single bond, X and Y do not simultaneously mean F.

The invention further relates to the use of these compounds as components of liquid-crystalline media and liquid-crystal and electro-optical display elements which contain the liquid-crystalline media according to the invention.

The compounds of the formula I can be used as components of liquid-crystalline media, in particular for displays based on the principle of the twisted cell, including its highly twisted variants, such as e.g. STN or SBE, the guest-host effect, the effect of "deformation of aligned phases or the effect of dynamic scattering.

The invention was based on the task of finding new stable liquid-crystalline or mesogenic compounds which are suitable as components of liquid-crystalline media and in particular have a comparatively low viscosity and also a medium positive dielectric anisotropy.

It has now been found that compounds of the formula I are particularly suitable as components of liquid-crystalline phases. In particular, they have comparatively low levels Viscosities. With their help, stable liquid-crystalline phases with a wide mesophase range can be obtained, which are advantageous values for the optical and dielectric anisotropy, which are at the same time characterized by very favorable values for the specific resistance. As a result, clear advantages can be achieved, particularly in the case of media for active matrix displays or supertwist displays.

Similar compounds with a 2-substituted methylene cyclobutane group are already known. However, these have no liquid crystalline properties.

W.R. Dolbier, et al., Tetrahedron Letters 28 (14), 1491-1492, 1987, e.g. B. the preparation of 3-phenyl-l- (dif-luormethylene) -cyclobutane and 3-phenyl-2,2-difluoro-l-methylene-cyclobutane and cycloaddition of difluoroalkene on styrene.

With the provision of compounds of the formula I, the range of liquid-crystalline substances which are suitable for the production of liquid-crystalline mixtures from various technical points of view is also very broadly widened.

The compounds of formula I have a wide range of applications. Depending on the selection of the substituents, these compounds can serve as base materials from which liquid-crystalline phases are predominantly composed; but connections of the Formula I liquid-crystalline base materials from other classes of compounds can be added, for example, to influence the dielectric and / or optical anisotropy of such a dielectric and / or to optimize its threshold voltage and / or its viscosity.

The compounds of formula I according to the invention with a chiral group of the formula

X

where X and Y are different from one another and MG is a mesogenic radical,

are particularly suitable as dopants for chiral tuned smectic phases with ferroelectric properties.

In the pure state, the compounds of the formula I are colorless and form liquid-crystalline mesophases in a temperature range which is conveniently located for electro-optical use. They are stable chemically, thermally and against light.

The invention thus relates to the compounds of the formula I, in particular the optically active compounds of the formula I, in which X and Y are different from one another, and the compounds of the formula IA,

woπn

Ri alkyl with 1 to 15 carbon atoms, and

^~ ® ^~ ® ^~ ' ^~ © ^~ "€ /" ^or ""'.

The invention relates in particular to compounds of the formula I in which at least one of the radicals A ¹ and A ² is 1,4-phenylene, 1,4-cyclohexylene, pyrimidine-2,5-diy1 or pyridine-2 which is optionally substituted by fluorine , 5-diyl means.

The invention furthermore relates to the use of these compounds as components of liquid-crystalline media. The invention further relates to liquid-crystalline media containing at least one compound which is a group of the formula

in which L ¹ , L ² , X and Y have the meaning given, preferably a compound of the formula I, in particular chiral-toned media containing at least one optically active compound of the formula I.

Liquid crystal display elements, in particular electro-optical display elements, which contain such media, in particular matrix liquid crystal displays. For the sake of simplicity, Cbu = -CXY in the following means a radical of the formula

Cyc is a 1,4-cyclohexylene radical, Che is a 1,4-cyclohexylene radical, Dio is a 1,3-dioxane-2,5-diyl radical, Dit is a 1,3-di-hian-2,5-diyl radical, Phe is a 1,4-phenylene radical, PheF a 1,4-phenylene radical which is mono- or disubstituted by fluorine, Pyd a pyridine-2,5-diyl radical, Pyr a pyrimidine-2,5-diyl radical and Bi a bicyclo (2 , 2,2) octylene radical, where Cyc and / or Phe can be unsubstituted or mono- or disubstituted by F or CN.

The compounds of the formula I accordingly comprise compounds with two rings of the sub-formulas Ia to Ib:

R ⁱ -A ² -Cbu = CXY Ia

Connections with three rings of the sub-formulas Ic to If:

as well as connections with four rings of the sub-formulas Ig to In:

R ⁱ -A ⁱ -A ⁱ -A ² -Cbu = CXY Ig

Ri-Ai-Z -.- Ai-Z -.- A2-Z ² -Cbu = CXY _In

Among them, those of the sub-formulas Ia, Ib, Ic, Id, Ie, If, Ig, Ii and II are particularly preferred.

The preferred compounds of sub-formula Ia include those of sub-formulas laa to Iah:

R ¹ -Pyr-Cbu = CXY lad

Among them, those of the formulas laa, lab, lac, lad, laf and were particularly preferred.

The preferred compounds of sub-formula Ib include those of sub-formulas Iba to Ibm:

Ibe R ⁱ -Cyc-COO-Cbu = CXY Ibf

_R ι-A ⁱ -CH ₂ CH ₂ -Cbu = CXY Ibg

Ri-Ai-CH ₂ 0-Cbu = CXY Ibi

The preferred compounds of sub-formula Ic include those of sub-formulas Ica to Icm:

R ⁱ -Pyr-Phe-Cbu = CXY leg

R ⁱ -Cyc-Phe-Cbu ^ XY Ici

R ⁱ -Dit-Phe-Cbu = CXY Icj

R ⁱ _Che-Phe-Cbu = CXY Ici

Among them, those of the formulas Ica, Icc, Icd, Ice, Ici and Icj are particularly preferred. The preferred compounds of sub-formula Id include those of sub-formulas Ida to Idm:

The preferred compounds of sub-formula le include those of sub-formulas Iea to Iek:

Iek The preferred compounds of the sub-formula If include those of the sub-formulas Ifa to Ifp

R ⁱ -Dio-Cyc-Z ⁱ -Cbu = CXY If j

R ⁱ _Phe-Cyc-Z ⁱ -Cbu = CXY Ifk

The preferred compounds of the formulas Ig include those of the formulas Iga to Igf:

In the compounds of the formulas above and below, the radicals X and Y are preferably different from one another. The terminal group Cbu = CXY thus preferably means a group of the formulas 1 to 8:

Cbu = CHF 1

Cbu = CHCl 2

Cbu = CHCF ₃ 3

Cbu = CFCl 4

Cbu = CF-CF ₃ 5

Cbu = CCl-CF ₃ 6 Cbu = CF ₂ 7

Cbu = CCl ₂ 8

R ¹ is preferably alkyl, furthermore alkoxy. A ¹ or A ^{2 are} preferably Phe, Cyc, Che, Pyr or Dio. The compounds of the formula I preferably contain no more than one of the radicals Bi, Pyd, Pyr, Dio or Dit.

Also preferred are compounds of the formula I and all sub-formulas in which A ¹ and / or A ^{2 is} 1,4-phenylene which is mono- or disubstituted by F or monosubstituted by CN. In particular, these are 2-fluoro-1,4-phenylene. 3-fluoro-l, 4-phenylene and 2,3-difluoro-l, 4-phenylene, 2,6-difluoro-l, 4-phenylene, 3,5-difluoro-l, 4-phenylene and 2-cyano -l, -phenylene and 3-cyano-l, 4-phenylene.

Particular preference is given to those compounds of the formulas I in which A ^{2 is} 1,4-phenylene which is unsubstituted or mono- or disubstituted by F. Z ¹ and Z ^{2 are} preferably a single bond, -CO-O-, -O-CO- and -CH ₂ CH -, in the second place preferably -CH ₂ 0-and

-OCH ₂ -.

If R ^{1 is} an alkyl radical or an alkoxy radical, this can be straight-chain or branched. It is preferably straight-chain, has 2, 3, 4, 5, 6 or 7 carbon atoms and accordingly preferably means ethyl, propyl, butyl, pentyl, hexyl, heptyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy or heptoxy, also methyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, methoxy, octoxy, nonoxy, decoxy, undecoxy, dodecoxy, tridecoxy or tetradecoxy.

Oxaalkyl preferably means straight-chain 2-oxapropyl (= methoxymethyl), 2- (= ethoxymethyl) or 3-oxabutyl (= 2-methoxyethyl), 2-, 3- or 4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl, 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl.

If R ^{1 is} an alkenyl radical, this can be straight-chain or branched. It is preferably straight-chain and has 2 to 10 carbon atoms. Accordingly, it means especially vinyl, prop-1-, or prop-2-enyl, but-1-, 2- or but-3-enyl, pent-1-, 2-, 3- or pent-4-enyl, hex -1-, 2-, 3-, 4- or

Hex-5-enyl, hept-1-, 2-, 3-, 4-, 5 or hept-6-enyl, oct-1-, 2-, 3-, 4-, 5-, 6- or oct -7-enyl, non-1-, 2-, 3-, 4-, 5-, 6-, 7- or non-8-enyl, dec-1-, 2-, 3-, 4-, 5- , 6-, 7-, 8- or Dec-9-enyl. If R 1 is an alkyl radical in which one CH ₂ group has been replaced by -0- and one has been replaced by -CO-, these are preferably adjacent. Thus they contain an acyloxy group -C0-0- or an oxycarbonyl group -0-C0-. Preferred

.- Wise, these are straight-chain and have 2 to 6 carbon atoms. Accordingly, they mean especially acetyloxy, propionyloxy, butyryloxy, pentanoyloxy, hexanoyloxy, acetyloxymethyl, propionyloxymethyl, butyryloxymethyl, pentanoyloxymethyl, 2-acety- loxyethyl, 2-propionyloxyethyl, 2-butyryloxyethyl, 3-acety-

_1Q loxypropyl, 3-propionyloxypropyl, 4-acetyloxybutyl, methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl, ethoxycarbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl, 2- (methoxycarbonyl) ethyl, 2- (ethoxacarbonyl Propoxy car

» ₅ bonyl) ethyl, 3- (methoxycarbonylpropyl, 3- (ethoxycarbonyl) propy1, 4- (methoxycarbonyl) -buty1.

If R ^{1 is} an alkenyl radical in which a CH ₂ group has been replaced by CO or CO-O or 0-CO-, this can be straight-chain or branched. It is preferably straight-chain and has 4 to 13 carbon atoms. Accordingly, it means in particular acryloyloxymethyl, 2-acryloyloxyethyl, 3-acryloyloxypropyl, 4-acryloyloxybutyl, 5-acryloyloxypentyl, 6-acrylic-loyloxyhexyl, 7-acryloyloxyheptyl, 8-acryloyloxyoctyl, 5 9-acryloyloxynyloxyloxyloxylonyloxyloxynonyl, methoxyloxynonyl - thyl, 2-methacryloyloxyethyl, 3-methacryloyloxypropyl, 4-methacryloyloxybutyl, 5-methacryloyloxypentyl, 6-methacryloyloxyhexyl, 7-methacryloyloxyheptyl, 8-methacryloyloxyoctyl, 9-methacryloyloxynonyl. 0 Compounds of the formula I which have wing groups R 1 suitable for polymerization reactions are suitable for the preparation of liquid-crystalline polymers.

Compounds of the formulas I with branched wing groups R ¹ can occasionally be of importance because of their better solubility in the customary liquid-crystalline base materials, but in particular as chiral dopants if they are optically active. Smectiehe connections of this type are suitable as components for ferroelectric materials.

10 compounds of the formula I with S _A phases are suitable, for example, for thermally addressed displays.

Branched groups of this type usually do not contain ₅ more than one chain branch. Preferred branched radicals R ¹ are isopropyl, 2-butyl (= 1-methylpropyl), isobutyl (= 2-methylpropyl), 2-methylbutyl, isopentyl (= 3-methylbutyl), 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl, 2-propylpentyl, isopropoxy, 2-methylpropoxy, 2-methylbutoxy, 3-methylbutoxy, _2n 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy, 1-methylhexoxy, 1-methylheptoxy, 2-oxa-3-methylbutyl, 3 -Oxa-4-methylpentyl, 4-methylhexyl, 2-nonyl, 2-decyl, 2-dodecyl, 6-methyloctoxy, 6-methyloctaroyloxy, 5-methylheptyloxycarbonyl, 2-methylbutyryloxy, 3-methylvaleryloxy, 4-methylhexanoyloxy , ₂₅ 2-chloropropionyloxy, 2-chloro-3-methylbutyryloxy, 2-chloro-4-methylvaleryloxy, 2-chloro-3-methylvaleryloxy, 2-methyl-3-oxapentyl, 2-methyl-3-oxahexyl.

Contain preferred optically active compounds of formula I.

30 as a chiral residue a group of the formula where X and Y are different from each other.

If R ^{1 represents} an alkyl radical in which two or more CH ₂ groups have been replaced by -0- and / or -C0-O-, this can be straight-chain or branched. It is preferably

10 branches and has 3 to 12 carbon atoms. Accordingly, it means especially bis-carboxy-methyl, 2,2-bis-carboxy-ethyl, 3,3-bis-carboxy-propyl, 4,4-bis-carboxy-butyl, 5,5-bis-carboxy-pen- tyl, 6, 6-bis-carboxy-hexyl, 7,7-bis-carboxy-heptyl, 8,8-bis-carboxy-octyl, 9, 9-bis-carboxy-nonyl, 10,10-bis-carboxy-

₁₅ decyl, bis (methoxycarbonyl) methyl, 2,2-bis (methoxycarbonyl) ethyl, 3,3-bis (methoxyearbony1) propyl, 4,4-bis (methoxycarbonyl) butyl , 5, 5-bis (methoxycarbonyl) pentyl, 6,6-bis (methoxycarbonyl) hexyl, 7,7-bis (methoxycarbonyl) heptyl, 8,8-bis (methoxycarbonyl) oetyl. Bis- (ethoxycar-

_ _n bonyl) methyl, 2,2-bis (ethoxycarbonyl) ethyl, 3,3-

Bis (ethoxycarbony1) propyl, 4,4-bis (ethoxycarbony1) butyl, 5,5-bis (ethoxycarbonyl) hexyl.

Compounds of the formula I which are used for polycondensation - _j . suitable wing groups R ¹ are suitable for the presentation of liquid-crystalline polycondensates.

Formula I includes both the racemates of these compounds and the optical antipodes and mixtures thereof. 0

Ri, F, Cl, CF ₃ , 0CF ₃ or OCF ₂ preferably denotes H, in particular when X and Y mean H or alkyl. V and L ² are preferably identical and denote F, Cl or H, in particular H.

Among these compounds of the formula I and the sub-formulas, preference is given to those in which at least one of the radicals contained therein has one of the preferred meanings indicated.

In the compounds of the formula I, those stereoisomers are preferred in which the rings Cyc and piperidine are trans-1,4-disubstituted. Those of the formulas mentioned above which contain one or more groups Pyd, Pyr, Dit and / or Dio each enclose the two 2,5-position isomers.

Particularly preferred compounds of the formula I which have a group of the formula 1 are those of the sub-formulas Ila to Iln:

alkyl-Cyc-Cbu = CHF Ila alkyl-Phe-Cbu = CHF Ilb alkyl-Cyc-Cyc-Cbu = CHF Ilc alkyl-Cyc-Phe-Cbu = CHF ^' ild alkyl-Cyc-CH ₂ CH ₂ -Cbu = CHF Ile alkyl-Phe-CH ₂ CH ₂ -Cbu = CHF Ilf alkyl-Phe-CO-0-Cbu = CHF Ilg alkyl-Cyc-CO-0-Cbu = CHF Ilh alkyl-Cyc-Phe-C≡C-Cbu = CHF Ili alky1-Cyc-Phe-CH ₂ CH ₂ -Cbu = CHF 11j alkyl-Cyc-Cyc-CH ₂ CH ₂ -Cbu = CHF Ilk alkyl-Phe-Phe-CH ₂ CH ₂ -Cbu = CHF 111 alkyl-Cyc-CH ₂ CH ₂ -Cyc-Cbu = CHF order alkyl-Cyc-PheF-Cbu = CHF Iln

Particularly preferred compounds of the formula I which have a group of the formula 2 are those of the sub-formulas I2a to I2o:

alkyl-Phe-Cbu = CHCl I2a alkyl-Cyc-Cbu = CHCl I2b alkyl-Cyc-Phe-Cbu = CHCl I2c alkyl-Cyc-Cyc-Cbu = CHCl I2d alkyl-Phe-Phe-Cbu = CHCl I2e alkyl-Phe- CH ₂ CH ₂ -Cbu = CHCl I2f alkyl-Cyc-CH ₂ CH ₂ -Cbu = CHCl I2g alkyl-Cyc-CO-0-Cbu = CHCl I2h alkyl-Phe-CO-0-Cbu = CHCl I2i alkyl-Cyc- Phe-C≡C-Cbu = CHCl 12j alkyl-Cyc-Phe-CH ₂ CH ₂ -Cbu = CHCl I2k alkyl-Cyc-Cyc-CH ₂ CH ₂ -Cbu = CHCl 121 alkyl-Phe-Phe-CH ₂ CH ₂ -Cbu = CHCl I2m alkyl-Cyc-CH ₂ CH ₂ -Cyc-Cbu = CHCl I2n

alkyl-Cyc-PheF-Cbu = CHCl I2o

Particularly preferred compounds of the formula I which contain a group of the formula 7 are those of the sub-formulas I7a to l7o:

alkyl-PheF-Cbu = CF ₂ 17a alkyl-Cyc-Cbu = CF ₂ I7b alkyl-Cyc-Phe-Cbu = CF ₂ I7c alkyl-Cyc-Cyc-Cbu = CF ₂ I7d alkyl-Phe-Phe-Cbu = CF ₂ I7e alkyl-Phe-CH ₂ CH ₂ -Cbu = CF ₂ I7f alkyl-Cyc -CH ₂ CH ₂ -Cbu = CF2 I7g alkyl-Cyc-CO-0-Cbu = CF ₂ I7h alkyl-Phe-CO-0-Cbu = CF ₂ I7i alkyl-Cyc-Phe-G≡C-Cbu = CF ₂ 17 y alkyl-Cyc-Phe-CH ₂ CH ₂ -Cbu = CF ₂ I7k alkyl-Cyc-Cyc-CH ₂ CH ₂ -Cbu = CF ₂ 171 alkyl-Phe-Phe-CH ₂ CH ₂ -Cbu = CF ₂ I7m alkyl-Cyc-CH ₂ CH ₂ -Cyc-Cbu = CF ₂ I7n alkyl-Cyc-PheF-Cbu = CF ₂ I7o

Particularly preferred compounds of the formula I which have a group of the formula 8 are those of the formulas I8a to I8o:

alkyl-Phe-Cbu = CCl ₂ I8a alkyl-Cyc-Cbu = CCl ₂ I8b alkyl-Cyc-Phe-Cbu = CCl ₂ I8c alkyl-Cyc-Cyc-Cbu = CCl ₂ I8d alkyl-Phe-Phe-Cbu = CCl ₂ I8e alkyl-Phe-CH ₂ CH ₂ -Cbu = CCl ₂ I8f alkyl-Cyc-CH ₂ CH ₂ -Cbu = CCl ₂ I8g alkyl-Cyc-CO-0-Cbu = CCl ₂ I8h alkyl-Phe-CO-0- Cbu = CCl ₂ I8i alkyl-Cyc-Phe-C≡C-Cbu = CCl ₂ 18j alky1-Cyc-Phe-CH ₂ CH ₂ -Cbu = CCl ₂ ^18k alkyl-Cyc-Cyc-CH ₂ CH ₂ -Cbu = CCl ₂ 181 alkyl-Phe-Phe-CH ₂ CH ₂ -Cbu = CCl ₂ 18m alkyl-Cyc-CH ₂ CH ₂ -Cyc-Cbu = CCl ₂ 18n alkyl- Cyc-PheF-Cbu = CCl ₂ I8o

In the above compounds of the sub-formulas Ila to Um, I2a to I2n, I7a to I7n and I8a to I8n, alkyl in each case mean alkyl or alkoxy groups with 1 to 12 carbon atoms.

The 1, cyclohexenylene group preferably has the following structures:

The compounds of the formula I are prepared by methods known per se, as described in the literature (for example in the standard works such as Houben-Weyl, Methods of Organic Chemistry, Georg-Thieme-Verlag, Stuttgart), under reaction conditions which are suitable for the reactions mentioned are known and suitable, and use can also be made of variants which are known per se and are not mentioned here in detail.

The compounds of formula I can, for example, in analogy to that of Dobier et al. (J. Am. Chem. Soc. 107 (12), 3626-31 (1985)) can be prepared by cycloaddition of alkenes onto styrene derivatives (cf. Scheme I):

I- ⁱ L2

The compounds of the formula I in which Z ² denotes -O-CO- can be obtained by esterification of 3-methylenecyclobutanoic acid according to scheme 2

Ri- (Ai-Zi) _m -A ² -OH + HOOC

The methylene cyclobutane carboxylic acid derivatives can be prepared from the corresponding nitriles with aqueous sodium hydroxide solution (e.g. Gripps et al. Am. Soc. __1 (1959), 2723-2728).

Furthermore, the compounds of the formula I can be obtained from the corresponding 3-substituted cyclobutanones by condensation with methane derivatives according to C. Burton et al., Tetrahedron Lett. 23. (24), 3003-6 (1988) and J. Fried, et al., Tetrahedron Lett. _25/4329 (1984) in the presence of phosphine einesw be produced (e.g. scheme 3)

Furthermore, the compounds of the formula I can be prepared by reducing a compound which otherwise corresponds to the formula I but which contains one or more reducible groups and / or C-C bonds instead of H atoms.

Suitable reducible groups are preferably carbonyl groups, in particular keto groups, furthermore, for example, free or esterified hydroxyl groups or aromatically bound halogen atoms. Preferred starting materials for the reduction correspond to formula I, but can be a cyclohexane ring or cyclohexanone ring instead of a cyclohexane ring and / or a -CH = CH group instead of a -CH ₂ CH ₂ group and / or instead of one -CH ₂ group contain a -CO group and / or instead of an H atom a free or a functionally modified (eg in the form of its p-toluenesulfonate) OH group. The reduction can be carried out, for example, by catalytic hydrogenation at temperatures between about 0 ° and about 200 ° and pressures between about 1 and 200 bar in an inert solvent, for example an alcohol such as methanol, ethanol or isopropanol, an ether such as tetrahydrofuran (THF) or dioxane, an ester such as ethyl acetate, a carboxylic acid such as acetic acid or a hydrocarbon such as cyclohexane. Suitable catalysts are suitably noble metals such as Pt or Pd, which are in the form of oxides (for example Pt0 ₂ , PdO) on a support

(e.g. Pd on carbon, calcium carbonate or strontium carbonate) or in finely divided form.

Ketones can also be prepared using the Clemmensen methods (with zinc, amalgamated zinc or tin and hydrochloric acid, expediently in an aqueous-alcoholic solution or in a heterogeneous phase with water / toluene at temperatures between about 80 and 120 °) or Wolff-Kishner (with hydrazine, expediently in the presence of alkali such as KOH or NaOH in a high-boiling solvent such as diethylene glycol or triethylene glycol at temperatures between about 100 and 200 °) to give the corresponding compounds of the formula I which contain alkyl groups and / or —CH ₂ CH ₂ bridges, be reduced.

Reductions with complex hydrides are also possible. For example, arylsulfonyloxy groups can be removed reductively with LiAlH ₄ , in particular p-toluenesulfonyloxy methyl groups can be reduced to methyl groups, advantageously in an inert solvent such as diethyl ether or THF Temperatures between about 0 and 100 °. Double bonds can be hydrogenated with NaBH ₄ or tributyltin hydride in methanol.

_c Compounds of the formula I which otherwise correspond to the formula I but which have 1,4-cyclohexenylene radicals instead of 1,4-phenylene radicals can be oxidized, for example, with DDQ (dichlorodicyanobenzoquinone) in a suitable solvent become.

10

Esters of the formula I can also be esterified by corresponding carboxylic acids (or their reactive derivatives), in particular formula IV, with alcohols or phenols (or their reactive derivatives), in particular formula V,

₁₅ or by the DCC method (DCC = dicyclohexylcarbodiimide) can be obtained.

The corresponding carboxylic acids and alcohols or phenols are known or can be prepared analogously to known _{processes? N} are produced.

Suitable reactive derivatives of the carboxylic acids mentioned are in particular the acid halides, especially the chlorides and bromides, and also the anhydrides, e.g. also “mixed anhydrides, azides or esters, in particular alkyl esters with 1-4 C atoms in the alkyl group.

Suitable reactive derivatives of the alcohols or phenols mentioned in particular the corresponding metal-alcoholic come - ^ _n late or phenolates, preferably of an alkali metal such as sodium or potassium, into consideration. The esterification is advantageously carried out in the presence of an inert solvent. Particularly suitable are ethers such as diethyl ether, di-n-butyl ether, THF, dioxane or anisole, ketones such as. As acetone, butanone or cyclohexanone, amides such as. B. DMF or phosphoric acid hexamethyl triamide, hydrocarbons such as benzene, toluene or xylene, halogenated hydrocarbons such. B. carbon tetrachloride, dichloromethane or tetrachlorethylene and sulfoxides such. B. dimethyl sulfoxide or sulfolane.

To prepare nitriles of the formula I, corresponding acid amides, for example those in which a CONH ₂ group is used instead of the CN radical, can be dehydrated. The

Amides can be obtained, for example, from corresponding esters or acid halides by reaction with ammonia. Suitable water-releasing agents are, for example, inorganic acid chlorides such as S0C1 ₂ , PC1 ₃ , PC1 ₅ , P0C1 ₃ , S0 ₂ C1 ₂ , C0C1 ₂ , and also P ₂ 0 ₅ , P ₂ S ₅ , A1C1 ₃ (for example as a double compound with NaCl ), aromatic sulfonic acids and sulfonic acid halides. You can do this in the presence or absence of an inert

Solvent work at temperatures between about 0 ° and 150 °; come as solvents e.g. Bases such as pyridine or triethylamine, aromatic hydrocarbons such as benzene, toluene or xylene or amides such as DMF into consideration.

For the preparation of the nitriles of the formula I mentioned above, corresponding acid halides, preferably the chlorides, can also be reacted with sulfamide, advantageously in an inert Solvents such as B. tetramethylene sulfone at temperatures between about 80 ° and 150 °, preferably at 120 °. After the usual work-up, the nitriles can be isolated directly.

Ethers of the formula I can be obtained by etherification of corresponding hydroxyl compounds, in particular of the formula VI or VII, preferably corresponding phenols, the hydroxyl compound advantageously first being converted into a corresponding metal derivative, for example by treatment with NaH, NaNH ₂ , NaOH, KOH, Na ₂ CO ₃ or K ₂ C0 _{3 is converted} into the corresponding alkali metal alcoholate or alkali metal phenolate. This can then be reacted with the corresponding alkyl halide, sulfonate or dialkyl sulfate, advantageously in an inert solvent such as. B. acetone, 1,2-dimethoxyethane, DMF or dimethyl sulfoxide or with an excess of aqueous or aqueous-alcoholic NaOH or KOH at temperatures between about 20 ° and 100 °.

To prepare nitriles of the formula I, corresponding chlorine, bromine or iodine compounds of the formula I can also be reacted with a cyanide, preferably with a metal cyanide such as, for. B. NaCN, KCN or Cu ₂ (CN) ₂ , e.g. B. in

Presence of pyridine in an inert solvent such as. B. DMF or N-methylpyrrolidone at temperatures between 20 ° and 200 °.

Compounds of the formula I in which A ¹ is substituted by at least one F atom and / or a CN group can also be obtained from the corresponding diazonium salts by exchanging the Diazonium group against a fluorine atom or against a CN group, for example by the methods of Schiemann or Sandmeyer, can be obtained.

Dioxane derivatives or dithiane derivatives of the formula I are conveniently prepared by reacting an appropriate aldehyde (or one of its reactive derivatives) with a corresponding 1,3-diol (or one of its reactive derivatives) or a corresponding 1,3-dithiol, preferably in the presence an inert solvent such as Benzene or toluene and / or a catalyst e.g. a strong acid such as sulfuric acid, benzene or p-toluenesulfonic acid, at temperatures between about 20 ° and about 150 °, preferably between 80 ° and 120 °. Acetals are primarily suitable as reactive derivatives of the starting materials.

Some of the aldehydes and 1,3-diols or 1,3-dithiols mentioned, and their reactive derivatives, are known, and in some cases they can be prepared without difficulty from standard compounds of organic chemistry from compounds known from the literature. For example, the aldehydes can be obtained by oxidation of corresponding alcohols or by reduction of nitriles or corresponding carboxylic acids or their derivatives, the diols by reduction of corresponding diesters and the dithiols by reaction of corresponding dihalides with NaSH.

In addition to one or more compounds according to the invention, the liquid-crystalline media according to the invention preferably contain 2 to 40, in particular, as further constituents 4 to 30 components. These media very particularly preferably contain 7 to 25 components in addition to one or more compounds according to the invention. These further constituents are preferably selected from nematic or nematogenic (monotropic or isotropic) substances, in particular substances from the classes of azoxybenzenes, benzylidene anilines, biphenyls, terphenyls, phenyl- or cyclohexylbenzoates, cyclohexane-carboxylic acid phenyl- or cyclohexyl esters, phenyl or cyclohexyl esters of cyclohexylbenzoic acid, phenyl or cyclohexyl esters of cyclohexylcyclohexane carboxylic acid, cyclohexylphenyl esters of benzoic acid, cyclohexane carboxylic acid or cyclohexylcyclohexane carboxylic acid, phenylcyclohexanes, cyclohexyl cyclohexyl cyclohexyl cyclohexyl cyclohexyl cyclohexyl cyclohexyl cyclohexyl cyclohexyl cyclohexyl cyclohexane cyclohexyl cyclohexyl cyclohexyl cyclohexyl cyclohexane cyclohexyl cyclohexyl cyclohexyl cyclohexyl cyclohexyl cyclohexyl cyclohexane Bis-cyclohexylbenzenes, 4,4'-bis-cyclohexylbiphenyls, phenyl- or cyclohexylpyrimidines, phenyl- or cyclohexylpyridines, phenyl- or cyclohexyldioxanes, phenyl- or cyclohexyl-1,3-dithiane, 1,2-diphenylethanes, 1,2-dicyclohexylethane, l-phenyl-2-cyclohexylethane, l-cyclo hexyl-2- (4-phenyl-cyclohexyl) ethane, 1-cyclohexyl-2-biphenylylethane, 1-pheny1-2-cyclohexylphenylethane, optionally halogenated stilbenes, benzylphenyl ether, tolanes and substituted cinnamic acids. The 1,4-phenylene groups in these compounds can also be fluorinated.

The most important compounds which are suitable as further constituents of media according to the invention can be characterized by the formulas 1, 2, 3, 4 and 5: R'-LER "1

R'-L-COO-E-R "2

R'-L-OOC-E-R "3

R'-L-CH ₂ CH ₂ -ER "4

R'-L-C - C-E-R "5

In formulas 1, 2, 3, 4 and 5, L and E, which may be the same or different, each independently

10 a bivalent radical from the group consisting of -Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -Pyr-, -Dio-, -G-Phe- and -G- Cyc and their mirror images formed group, wherein Phe unsubstituted or substituted by fluorine-substituted 1,4-phenylene, Cyc. trans-l, 4-cyclohexylene or 1, -cyclohexenylene, pyr pyrimi-, c din-2,5-diyl or pyridine-2,5-diyl, dio l, 3-dioxane-2,5-diyl and G 2- (trans-l, 4-cyclohexyl) -ethyl, pyrimidine-2,5-diyl, pyridine-2,5-diyl or 1,3-dioxane-2,5-diyl.

One of the radicals L and E is preferably Cyc, Phe or Pyr. _{? 0} is preferably Cyc, Phe or Phe-Cyc. The media according to the invention preferably contain one or more components selected from the compounds of the formulas 1, 2, 3, 4 and 5, in which L and E are selected from the group Cyc, Phe and Pyr and at the same time one or more components from _2e selected from the compounds of the formulas 1, 2, 3, 4 and 5, in which one of the radicals L and E is selected from the group Cyc, Phe and Pyr and the other radical is selected from the group -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc-, and optionally one or more components are selected

30th from the compounds of the formulas 1, 2, 3, 4 and 5, in which the radicals L and E are selected from the group -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc-.

In the compounds of the sub-formulas Ia, 2a, 3a, 4a and 5a, R 'and R "each independently represent alkyl, alkenyl, alkoxy, alkenyloxy or alkanoyloxy having up to 8 carbon atoms. In most of these compounds, R' and R" are each other different, one of these radicals is usually alkyl or alkenyl. In the compounds of the sub-formulas Ib, 2b, 3b, 4b and 5b, R "means -CN, -CF ₃ , -OCF ₃ , -OCHF ₂ , F, Cl or -NCS; R has the same for the compounds of the sub-formulas 1a to 5a and is preferably alkyl or alkenyl, but other variants of the proposed substituents in the compounds of the formulas 1, 2, 3, 4 and 5 are also common. Many such substances or mixtures thereof are commercially available. All of these substances can be obtained by methods known from the literature or by analogy.

The media according to the invention preferably contain in addition

Components from the group of compounds Ia, 2a, 3a, 4a and 5a (Group 1) also components from the group of compounds Ib, 2b, 3b, 4b and 5b (Group 2), the proportions of which are preferably as follows :

Group 1: 20 to 90%, in particular 30 to 90%, group 2: 10 to 80%, in particular 10 to 50%, the sum of the proportions of the compounds according to the invention and of the compounds from groups 1 and 2 giving up to 100%.

The media according to the invention preferably contain 1 to 40%, particularly preferably 5 to 30%, of compounds according to the invention. Also preferred are media containing more than 40%, in particular 45 to 90%, of compounds according to the invention. The media preferably contain three, four or five compounds according to the invention.

The media according to the invention are produced in a conventional manner. As a rule, the components are dissolved in one another, advantageously at elevated temperature. By means of suitable additives, the liquid-crystalline phases according to the invention can be modified so that they can be used in all types of liquid-crystal display elements which have hitherto become known.

Such additives are known to the person skilled in the art and are described in detail in the literature (H. Kelker / R. Hatz, Handbook of Liquid Crystals, Verlag Chemie, Weinheim, 1980). For example, pleochroic dyes for producing colored guest-host systems or substances for changing the dielectric anisotropy, the viscosity and / or the orientation of the nematic phases can be added.

The following examples are intended to illustrate the invention without limiting it, mp. = Melting point, cp. = Clearing point. Percentages above and below mean percentages by weight; all Temperatures are given in degrees Celsius. "Customary work-up" means: water is added, the mixture is extracted with methylene chloride, the mixture is separated off, the organic phase is dried, evaporated and the product is purified by crystallization and / or chromatography.

It also means:

K: crystalline solid state, S: smectic phase (the index indicates the phase type), N: nematic state, Ch: cholesteric phase, I: isotropic phase. The number between two symbols indicates the transition temperature in degrees Celsius.

DAST Diethylaminosulfur trifluoride

DCC dicyclohexylcarbodiimide

DDQ dichlorodicyanobenzoquinone

DIBALH diisobutyl aluminum hydride

HMTAP hexamethyltriaminophosphine

KOT potassium tertiary butanolate

PCC pyridinium chlorochromate

THF tetrahydrofuran

TPP triphenylphosphine pTSOH p-toluenesulfonic acid

example 1

Preparation of 3- [4- (trans-4-pentylcyclohexyl) phenyl] -1- (difluoromethylene) cyclobutane

A) 4- (trans-4-pentylcyclohexyl) vinylbenzene

A mixture of 1 mol of 4- (trans-pentylcyclohexyl) bromobenzene and 3 l of THF is mixed with 1 mol of BuLi at -70 ° C. A mixture of 0.5 mol of zinc bromide in 1 l of THF is then added to the reaction mixture and the mixture is stirred at -65 ° C. for 30 minutes. Then 1 mol of vinyl bromide and 0.022 mol of nickel (II) chloride / TPP are added.

The reaction mixture is stirred for 16 hours at room temperature and worked up as usual. The styrene derivative obtained is processed unpurified.

B) 3- [4- (trans-4-pentylcyclohexyl) phenyl] -2,2-dichlorocyclobutanone

A mixture of 0.25 mol of JLA, 23.0 g of zinc-copper (3% copper) and 800 ml of diethyl ether is mixed with 0.25 ml of trichloroacetyl chloride within 15 minutes and then stirred under reflux for 8 hours. After the usual work-up, the product is obtained, which is further processed without being cleaned. C) 3- [4- (trans-4-pentylcyclohexyl) phenyl] cyclobutanone

A mixture of 0.144 mol JLB, 0.53 mol zinc powder and 880 ml

Glacial acetic acid is stirred at room temperature for 17 hours. After the usual work-up, the product is obtained, which is further processed without being cleaned.

D)

A mixture of 0.3 mol of hexamethyltriaminophosphine and 50 ml of tetraglyme is added to a mixture of 1.5 mol of dibromide fluoromethane, 100 ml of tetraglyme at 0.degree. Then 0.075 and IC are added and the mixture is stirred at room temperature for 16 hours. After the usual work-up and crystallization from 100 ml of ethanol / ethyl acetate, the pure product, K 42 I, Δε +2.85, Δn 0.071 is obtained.

Analog are manufactured

3- [4- (trans-4-propylcyclohexyl) phenyl] -1- (difluoroethylene) cyclobutane

3- [4- (trans-4-ethylcyclohexyl) phenyl] -1- (difluoromethylene) cyclobutane

3- [4- (tans-4-butylcyclohexyl) phenyl] -1- (difluoromethylene) cyclobutane

3- [4- (trans-4-Hexylcyclohexyl) phenyl] -1- (difluoromethylene) cyclobutane

3- [4- (trans-4-heptylcyclohexyl) phenyl] -1- (difluoromethylene) cyclobutane 3- [4- [trans-4-ethylcyclohexyl) -2,3-difluorophenyl] -1- (difluoromethylene) cyclobutane

3- [4- [trans-4-propylcyclohexyl) -2,3-difluorophenyl] -1- (difluoromethylene) cyclobutane

3- [4- [trans-4-pentylcyclohexyl) -2,3-difluorophenyl] -1- (difluoromethylene) cyclobutane

3- [4- [trans-4-Hexylcyclohexyl) -2,3-difluorophenyl] -1- (difluoromethylene) cyclobutane

3- [4- [trans-4-heptylcyclohexyl) -2,3-difluorophenyl] -1- (difluoromethylene) cyclobutane

3- [4- [trans-4-ethylcyclohexyl) -2, 6-difluorophenyl] -1- (difluoromethylene) cyclobutane

3- [4- [trans-4-propylcyclohexyl) -2, 6-difluorophenyl] -1- (difluoromethylene) cyclobutane,

3- [4- [trans-4-pentylcyclohexyl) -2, 6-difluorophenyl] -1- (difluoromethylene) cyclobutane, K 29 I

3- [4- [trans-4-Hexylcyclohexyl) -2, 6-difluorophenyl] -1- (difluoromethylene) cyclobutane

3- [4- [trans-4-heptylcyclohexyl) -2,6-difluorophenyl] -1- (difluoromethylene) cyclobutane

3- (trans-4-ethylcyclohexyl) -1- (difluoromethylene) cyclobutane 3- (trans-4-propylcyclohexyl) -1- (difluoromethylene) cyclobutane 3- (trans-4-butylcyclohexyl) -1- (difluoromethylene) - cyclobutane 3- (trans-4-pentylcyclohexyl) -1- (difluoromethylene) -cyclobutane 3- (trans-4-hexylcyclohexyl) -1- (difluoromethylene) -cyclobutane 3- (trans-4-heptylcyclohexyl) -1- (difluoromethylene) -cyclobutane 3- (trans-4-octylcyclohexyl) -1- (difluoromethylene) -cyclobutane 3- [trans, trans-4- (4-ethylcyclohexyl) cyclohexyl] -1- (difluoromethylene) cyclobutane, Δn 0.073, Δε = 4.20

3- [trans, trans-4- (4-propylcyclohexyl) cyclohexyl] -1- (difluoromethylene) cyclobutane, Δn 0.058, Δε = 2.97

3- [trans, trans-4- (4-butylcyclohexyl) cyclohexyl] -1- (difluoromethylene) cyclobutane, K 40 S _B 99 N 104 I, Δε = 3.03, Δn = 0.067

3- [trans, trans-4- (4-pentylcyclohexyl) cyclohexy1] -1- (difluoromethylene) cyclobutane, K 38 S _B 99 N 112.1 I, Δε = 4.18, Δn = 0.072

3- [trans, trans-4- (4-hexylcyclohexyl) cyclohexyl] -1- (difluoromethylene) cyclobutane 3- [trans, trans-4- (4-heptylcyclohexyl) cyclohexyl] -1- (difluoro- methylene) cyclobutane

3- [4- (trans-4-ethylcyclohexyl) -2-fluorophenyl] -1- (difluoromethylene) cyclobutane

3- [4- (trans-4-propylcyclohexyl) -2-fluorophenyl] -1- (difluoromethylene) cyclobutane 3- [4- (trans-4-butylcyclohexyl) -2-fluorophenyl] -1- (difluor¬ methylene) cyclobutane

3- [4- (trans-4-pentylcyclohexyl) -2-fluorophenyl] -1- (difluoromethylene) cyclobutane 3- [4- (trans-4-hexylcyclohexyl) -2-fluorophenyl] -1- (difluoro- methylene) cyclobutane

3- [4- (trans-4-heptylcyclohexyl) -2-fluorophenyl] -1- (difluoromethylene) cyclobutane Example 2

Preparation of (4- [trans-4-propylcyclohexyl) phenyl) -3-isopropylidene cyclobutane carboxylic acid ester

To a mixture of 0.1 mol of 3-isopropylidene cyclobutane carboxylic acid ester (prepared according to Gripps et al. Am. Soc. Üi

(1959), 2723-2728) 0.1 mol of 4- (trans-4-propylcyclohexyl) phenol and 100 ml of dichloromethane give a mixture at 0 ° C

0.11 mol DCC and 50 ml dichloromethane. After stirring for 16 hours at room temperature, separating off the solid constituents and customary working up, the product is obtained.

The following are produced analogously:

given.

The mixtures thus obtained are filled into a test cell.

The "voltage holding ratio" of these cells is measured at room temperature HR (RT) and after heating to 100 ° C. HR (100).

The "holding ratio" was measured according to: G. Weber et al. Liquid Crystals 5_, 1320 (1989).

The compounds (1), (2) and (3) are therefore suitable for the production of mixtures with positive anisotropy of the dielectric constants and high values of the holding ratio, in particular for active matrix displays.

Claims

Δn_-40 claims

Methylene cyclobutane derivatives of the formula I.

U L2

in which

R- halogen, CN, CF ₃ , -OCF ₃ , -OCF ₂ H or an unsubstituted or an alkyl or substituted simply by CN, halogen or CF ₃

Alkenyl or perfluoroalkyl radical with up to 15 carbon atoms, one or more CH ₂ groups in these radicals each being independent of one another by -S-, - \ / """r><^ ~ '~ ^0- ' -CO -, -CO-O-, -O-CO- or -O-CO-O- can be replaced so that S and / or O atoms are not directly linked,

A ¹ and A ^{2 are} each independently one

(a) trans-1,4-cyclohexylene radical, in which one or more non-adjacent CH ₂ groups can also be replaced by -0- and / or -S-. (b) 1,4-phenylene radical, in which one or two CH groups can also be replaced by N,

(c) residue from the group 1,3-cyclobutylene, 1,3-bicyclo (1,1, l) pentylene, 1,4-cyclohexenylene, 1,4-bicyclo (2,2,2) octylene, piperidine-1 , 4-diyl, naphthalene-2, 6-diyl, decahydronaphthalene-2, 6-diyl and 1,

2,

3,4-tetrahydronaphthalene-2,6-diyl,

where the radicals (a) and (b) can be substituted one or more times by CN or halogen,

H and L ² each H, F or Cl,

Zi and Z ² each independently of one another -CH ₂ CH ₂ -,

-CsC-, -CH ₂ 0-, -0CH ₂ -, -CO-O-, -O-CO-, -CH = N-, -N = CH-, -CH ₂ S-, -SCH ₂ -, a single bond or an alkylene group with 3 to 6 C atoms, in which a CH ₂ group is also represented by -0-, -CO-O-,

-O-CO-, -CHHalogen- or -CHCN- can be replaced,

X and Y are each independently of one another F, Cl, Br CF ₃ , CN, C0 ₂ or alkyl having 1 to 6 C atoms, one of the radicals X and Y also H, and

m 0, 1, 2 or 3

mean. with the proviso that when m = 0, A ² 1,4-phenylene and Z ² a single bond X and Y do not simultaneously mean F.

Derivatives of formula I according to Claim 1, in which at least one of the radicals A ¹ and A ² , 1,4-phenylene, 1,4-cyclohexylene, pyrimidine, 2-5, diyl or pyridine-2,5 optionally substituted by fluorine -diy1 means.

Derivatives according to claim 1 of formula IA

wherein

Ri alkyl with 1 to 15 carbon atoms

n 0 or 1

mean.

4. Optically active methylene cyclobutane derivatives of the formula I, characterized in that X and Y are different from one another.

5. Use of the compounds of formula I as components of liquid-crystalline media for electro-optical displays.

6. Liquid-crystalline medium with at least two components, characterized in that at least one component

IL ²

nente a group of the formula wherein L ¹ , L ² , X and Y has the meaning given.

7. Liquid-crystalline medium according to claim 6, characterized in that at least one component is a compound of formula I.

8. Chiral-tutted liquid-crystalline medium with at least one achiral component and at least one chiral component, characterized in that at least one chiral component is an optically active methylene cyclobutane derivative of the formula I according to claim 4.

9. Electro-optical display, characterized in that it contains a liquid-crystalline medium according to one of claims 6 to 8 as a dielectric.

10. Matrix liquid crystal display according to claim 9, characterized in that it contains as a dielectric a liquid-crystalline medium according to claim 6, 7 or 8.